Inexpensive slender linear motion potentiometer



R c: PARKINSON ETAL 3,348,185 INEXPENSIVE SLENDER LINEAR MOTION POTENTIOMETER zzw/s .1 055,404:

Filed Oct. 5, 1966 United States Patent Ofitice 3,348,185 Patented Oct. 17, 1967 3,348,185 INEXPENSIVE SLENDER LINEAR MOTION POTENTIOMETER Robert C. Parkinson, Eugene A. Marks, and Donald L. Gaa, Riverside, and Lewis J. De Back, Bloomington, Calitl, assignors to Bourns, Inc., a corporation Filed Oct. 5, 1966, Ser. No. 584,505 6 Claims. (Cl. 338-183) ABSTRACT OF THE DISCLOSURE The invention herein described in preferred exemplary form pertains to potentiometers of the class devised for furnishing an electrical representation of the extent of movement or translation of an object in the direction of a selected axis or along such axis. That class of potentiometers is in the art commonly designated linear motion otentiometers. More specifically, the present invention pertains to improvements whereby the cost of a potentiometer within the noted class is considerably reduced via gross reduction in the cost of components and the cost of fabricating the components into a completed potentiometer, while concurrently notably improving the structural and electrical characteristics of the instrument whereby mechanical and electrical testing and inspection during manufacture are greatly facilitated and the instrument made to be much more rugged and capable of successfully withstanding greater abuse, relative to prior art potentiometers of the class.

Briefly, the improvements are principally attained by mounting the operating components on the exterior of an extruded body or support which serves as a guide for reciprocable members and serves also to present exposed surfaces on which resistance element and conductor bar means are affixed, the arrangement being such that the assembled principal operating and electrical parts are exposed for mechanical and electrical inspection and further is such that an actuator rod of much larger diameter may be employed than in the prior art instruments. Further, the extrusion and attachments are so shaped as to be inexpensive and to be easily fitted into a cylindrical tubular housing which provides a very strong and inexpensive enclosure for the operating means. Thus the noted extrusion or support is shaped to present a set of longitudinally-extending channels or grooves, larger centrally-located one of which serves as a guideway in which a contact-carrying post or slider is supported and restrained to axial reciprocatory (linear) movements, and in other of which groves resistance-element means are secured but exposed for inspection and functional cooperation with contact devices carried by the slider. Further, the extrusion is shaped with an arcuate substantialy semi-cylindrical surface complementary with the inner surface of the noted tubular housing member, the arcuate semi-cylindrical surface being interrupted by channels in which insulated conductors may be disposed. The conductors serve for establishing electrical communication with resistance element means. As will be made evident, all of the noted longitudinally-extending channels are formed during the extrusion of the body or support, whereby the support is made by merely severing a desired length from a long extrusion or bar. Thus potentiometers of various lengths may be readily and inexpensively made, using the same extrusion stock for bodies or supports of various lengths. The same economy is effected relative to tubular housings of various lengths. Since, in general, much machining of guideways, and stocking of various lengths of bodies or supports for linear motion potentiometers having various and sundry diflerent elfective strokes has in the past been required, it is evident that a construction according to the invention permits considerable cost savings to be effected.

Further, according to the invention, the noted inexpensive extruded body member is so formed as to both hold captive the noted slider, and to very accurately guide the slider, while permitting ready access to the slider contacts, the resistance element means, and longitudinally-extending return conductor means which serve to establish electrical communication with the traveling contact means on the slider, and electrical terminal means. Further, the shape and nature of the stationary body or base of the potentiometer, formed as an extrusion, is such as to make the potentiometer very small in transverse dimension and to permit the use of an actuator rod of much larger diameter, relative to maximum transverse dimension of the potentiometer structure, than has ever before been achieved in the prior art. For example, for a potentiometer having a maximum transverse dimension of 0.500 inch (diameter, in this case), the actuator rod may be of 0.188 diameter; whereby both the actuator and the housing may be extraordinarily stiff.

Since in many applications of linear motion potentiometers it is deisred or even required to furnish two out put signals or potentials both of which vary in accord with displacements of the slider relative to the body or housing, the exemplary potentiometer hereinafter described in detail is formed to accommodate or meet the noted requirement. However, the structure is not in any sense restricted to dual-output applications. Further, as constructed in the exemplary and preferred form, the structure is such as to readily and easily me modified to permit tapping of the resistance element means at any desired location along the active extent of the element.

The foregoing brief general description of the invention makes it evident that it is a principal object of the invention to provide general improvements in linear motion potentiometers whereby the cost of production thereof is substantially lessened with concurrent increase in durability, strength and effectiveness.

Another object of the invention is to provide a linear motion potentiometer of such construction as to readily permit visual examination and electrical and mechanical inspection and testing of the principal electrical and operating mechanical components as a sub-assembly unit prior to incorporation into a completed final assembly.

Other advantages and objects of the invention will here inafter be set out or made evident in the appended claims and following detailed description of a presently-preferred exemplary potentiometer embodying the invention, the description having reference to the accompanying drawings forming a part of this specification.

In the drawings:

FIGURE 1 is a plan view, partly in section, of the noted exemplary potentiometer, the scale being grossly enlarged in the interest of illustrating detail and parts being broken away for the same reason;

FIGURE 2 is a tranverse sectional view taken as indicated by the broken line 2-2 in FIGURE 1, showing details of a contact-supporting slider device and contact means carried thereon, and further showing the relationship of the contact means to resistance-element means and 63 3 arrangement of support means and operating parts; and

FIGURE 4 is a fragmentary face view of part of the structure shown in plan view in FIGURE 1, with parts broken away to reveal internal details, the drawing being on reduced scale.

Referring first to FIGURE 1, the instrument as an entirety is labeled 10. Principal components include an elongate tube or cylinder 12 which serves as an inexpensive light-weight, very strong, and stiff structure to house operating components and which augments the longitudinal strength and rigidity of other means of the instrument. As is evident, the cylinder 12 may serve to define a longitudinal axis of the instrument, in the directions of which axis linear movements of movable parts may be specified. Disposed in cylinder 12 is an elongate stiff support 14 formed as a section of an extruded member, preferably of metal, and of cross-sectional configuration clearly indicated in FIGURES 2 and 3. In the electrical terminal end of the instrument (left end, as shown in FIGURE 1) an insulative plug 16 of circular shape abuts against one end of the elongate support 14; and at the opposite or actuator end of the instrument a second but longer cylindrical plug-like member, herein termed a bearing, 18, is disposed with its inner end abutting against the support 14. Bearing 18 is axially bored to accommodate for reciprocation a complementary portion of an actuator 20 herein shown as a plain elongate cylindrical rod. Thus the bore of bearing 18 is such as to provide a working fit with rod 20, and the bore is sealed by an O-ring 22 fitted in an internal annular groove in the bearing as indicated. Bearing 18 is retained in the end of cylinder 12 by peening the end of the cylinder into a receiving formation on the bearing as indicated, whereby the bearing is gripped and held against movement relative to the cylinder.

Support 14 is held against rotation in the housing cylinder 12 and relative to the bearing 18 by means of pins, such as 24, 26, which are embedded in the inner end portion of the bearing 18 and protrude and tightly fit in complementary holes bored in the adjacent end portion of the support. Similarly, terminal end plug 16 is properly positioned relative to support 14 and affixed thereto by cooperating pins each engaging both of those members.

Support 14, as noted, has a lower face of the form of a portion of a solid cylinder, of radius slightly less than that of the inner surface of cylinder 12. The support is desirably insulated from cylinder 12 by means of insulation, for example by one or more layers of pressure-sensitive insulative sheet or tape, indicated at 28 (FIGURES 2 and 3) disposed along the appropriate extent of the interior of the cylinder. The support is formed with elongate opposed curved flanges 14e and 14 each of which along its interior surface presents portions of a guide surface of arcuate cross-sectional shape as indicated in FIGURES 2 and 3. As best indicated in FIGURE 2, the support also has formed therein other longitudinally extending grooves including a groove or guideway 14g, elongate grooves or slots 14w, 14x, 14y and 142 in the outer (lower) face for optional reception of conductors, and resistance element-receiving trough-like grooves 14r, 14s. Further, the support 14 is formed to provide, along the upper outer extremities of flanges Me and 14 a pair of surfaces for supporting a pair of elongate strip-like return conductors presently to be described.

Supported and guided by the support 14 for longitudinal (axial) reciprocation along and in the guiding confines provided by flanges 14e, 14] and guideway 14g is a slider device 32 (FIGURE 3) comprising an insulative block 34 (FIGURE 2) which as indicated in FIGURES 1, 2 and 3 is short relative to the overall length of support 14 but which is long enough to have effective guided relationship with the flanges and internal groove of the support. Further, the cross-sectional configuration of the lower part of block 32 is complementary to that of the internal surface of support 14. Slider block 34 further is provided with an axial bore 34a (FIGURE 2) through which a reduced-diameter end portion of actuator rod 20 extends. The reduction of diameter of rod 20 provides a shoulder 20s (FIGURE 1) against which a horned or star stop washer 36 fits, the latter washer fitting on the reduced portion of the rod and serving by means of its horns to restrict or limit outward movement of rod 20 and prevent slider device 3 2 from colliding with bearing 18 as rod 20 is moved outwardly. The slider block 34 is mounted on the reduced-diameter portion of rod 20 between two plain washers 40, 40, each of which washers bears face to face with a respective end of the block. The plain washers are held in place between an E retainer 38 at one end of the block, and a bowed washer 42 at the other end, the bowed washer being held under compression between the adjacent washer 40 and a second E retainer 44. The E retainers are disposed in annular grooves in rod 20. Thus the slider block 32 and its appurtenances are constrained to move with rod 20, the inward movements (to the left in FIGURE 1) being limited by the inner end of rod engaging the inner face of terminal plug 16, and movements in the opposite direction being limited by stop washer 36 engaging bearing 18 as previously noted.

Disposed in the elongate troughs or grooves 141' and 14s (FIGURE 2) of support 14 and insulated from the latter by insulative tape T as indicated are respective resistance elements 46 and 48, each of which may comprise an insulated-wire mandrel and a helical winding of resistance wire. The resistance elements are secured in place by self-setting adhesive applied to the insulation in the groove and to the lower part of the element, in each case.

Mounted on respective outer shoulders of the flanges 14a and 14 of the support 14 are first and second bare return-conductor strips 50 and 52 which are insulated from the support by adhesive insulative tape T. The conductors are adhesively secured to the insulation, as by epoxy resin cement or like material. Thus the bare conductive strips 50 and and 52 are parallel to the axis of the instrument and to the resistance elements 46 and 48.

Embedded in the upper enlarged head of slider block 34 are opposed arcuate downwardly-extending rigid horns 54 and 56 (FIGURES 2 and 3), the horns forming support means comprised in first and second contact devices carried by the slider block. Each of horns 54 and 56 supports and carries aflixed thereto a respective integral resilient contact structure, 58, 59, formed from resilient sheet metal. Each contact structure comprises a curved body arranged to fit on and be secured to a respective horn, and integral contact arms such as 59a, 59b and 590 (FIGURE 4). The dual contact arms, such as arms 59a and 59b, terminate in bare contacts which are arranged to brush on a respective one of conductor strips 50 and 52 as indicated; and the single contact arms, such as contact arm 59c, terminate in respective single contacts arranged to brush on the adjacent one of resistance ele ments 46 and 48. Thus in each instance there is established a direct electrical connection from the brushing point of a contact on a resistance element, and the respective collector conductor strip.

Terminal connections are made to the ends of each of the resistance elements 46 and 48, and to an end of each of the collector conductors 50 and 52, by insulated wires '62, 62 64, 64 and 66, 68, respectively, as indicated at the terminal (left) end of the instrument in FIGURE 1, the ends of the terminal wires 62, 64, 66 and 68 being brazed or soldered to their respective electrical components, as indicated at the terminal end of the instrument and wires 62 and 64 passing through respective ones of grooves 14x and 14y and transverse bores or slots to the distant ends of the resistance elements. The terminal wires are collected and sealed in a conduit 70, the inner flared end of which is embedded in adhesive resin potting compound which is used to seal the left or terminal end of the instrument and to anchor support 14 and the other fixed components of the instrument firmly in place in the cylinder 12.

In addition to the aforementioned terminal wires, provision is made according to the invention whereby tap or intermediate terminal connections may be made to selected points along the extent of either or both of the resistance elements. Thus, as indicated in FIGURE 4, a slot 142 may be milled or formed in the support 14, transversely of the latter and interconnecting the trough or groove 14s in which the resistance element is seated, and one or both of the adjacent longitudinally-extending grooves 14w and 14x, whereby a tap connection 482 (FIGURE 4) may he made from a terminal conductor 72 which conductor is disposed in groove 14w for example. Other tap connections may be similarly made, to either or both of the resistance elements, at any desired location, using terminal Wires disposed in the several grooves 14w, 14x, 14y, and 142 (FIGURE 3). As is indicated, the tap-connection terminal wires are potted in place in the grooves, and at the terminal end of the instrument extend through conduit 70.

It is made evident in the preceding description that installation of the resistance elements, return conductor strips, terminal Wires and slider device is easily accomplished due to their exposed locations relative to support 14. Further, it is evident that with support 14, electrical components 46, 48, 50 and 52, hearing 18 and plug 16 assembled as a subassernbly unit, with slider device 32 and its appurtenances in place and operatively connected to actuator rod 2% and with the terminal Wires connected, both electrical and mechanical inspections of the operating components of the instrument may be readily made, the parts at that stage of manufacture being openly visible and exposed for examination. Following completion of such inspection and testing the noted su-bassembly as a unitary structure is readily inserted into housing cylinder 12 and pressed home therein, with the plotting resin P applied as needed or forced into the desired regions and there permitted to cure.

Also made evident by the description are the facts that by utilization of elongaate extrusions as stock from which such members as cylinder 12, support 14 and slider block 34 are made, instruments of various effective displacements or lengths may be inexpensively made with a minimum expenditure of time and machine operations. Further, as is made evident, by disposing the elongate resistance elements and collector conductors in exposed locations on the outside of a support, those components are most easily assembled and made available for quick and easy adjustment and inspection, and possible replacement if found to fail to pass inspection. Further, and of great importance, by utilizing an extruded support which by itself is stiff, and a closely conforming cylindrical housing which provides a maximum of stiffness or longitudinal strength, instruments of very small overall diameter but of exceptional length may be made without any sacrifice in economy of manufacture. Further, the structure is such as to permit use of an actuator rod of exceptionally large diameter relative to housing diameter, whereby stiffness of the actuator is greatly increased. An exemplary highly successful instrument has an overall outside diameter of one-half inch and a rod diameter of inch. In those instances or application in which with a very long instrument exceptional transverse vibration may be encountered additional longitudinal stiffness is readily obtained by inserting the instrument in a closely fitting jacket tube of appropriate length and cross-section. Additionally, while the exemplary instrument is conveniently made as a dual-potentiometer device, to conform to the requirements of many applications and whereby a spare potentiometer is made available in those applications in which but a single unit is required, it is evident that one potentiometer unit may be omitted, or formed as an operative or dummy unit with no electrical connections.

In the light of the preceding detailed disclosure of a preferred exemplary embodiment of the invention changes and modifications within the true spirit and scope of the invention will occur to others. Accordingly, it is not desired to restrict the invention to specific details of the exemplary structure other than is required by specific limitations defined in the appended claims.

We claim:

. 1. An elongate slender linear potentiometer characterized by small maximum transverse dimension and inexpensive construction, said potentiometer comprising:

first means, including housing means formed principally as an elongaate cylinder and a bearing in a first end thereof;

second means, including an elongate support means having an elongate exterior surface complementary with and closely fitting a portion of the elongate interior surface of said cylinder, said support means presenting along its exterior an elongate groove and presenting further an elongate guideway;

third means, including a resistance element supported in said elongate groove with a contact surface exposed for brushing of a contact thereon, an elongate return conductor supported on the exterior of said support means generally parallel to said resistance element, and terminal means for said element and said conductor;

fourth means, including rectilinearly movable means comprising a slider device operable along and engaging in said guideway to be guided thereby, and said slider device comprising a conductive contact device having a first contact in brushing engagement with said elongate conductor and a second contact in brushing engagement with the said contact surface of said resistance element;

and fifth means, including reciprocatory actuator rod means extending through said bearing and connected to said slider device for reciprocation of the latter along said guideway;

whereby said second, third, fourth and fifth means can be assembled to form an operable subassembly and subjected to operating and electrical tests with the components thereof exposed for visual inspection and access, prior to incorporation of said second, third and fourth means in said cylinder and assembly with said first means to form a complete potentiometer.

2. A potentiometer according to claim 1, in which said terminal means include conductors extending out of the second end of said cylinder, and said first means including means plugging said second end of said cylinder and retaining said second and third mans in said cylinder.

3. A potentiometer according to claim 2, in which said third means includes a second resistance element supported in a second elongate groove in said support means with an exposed contact surface thereon and further includes a second elongate return conductor supported on the exterior of said support means, and terminal means for said second element and said second conductor, and in which said slider device comprises a second contact device having contacts respectively brushing on said second element and said second return conductor, whereby to provide twin potentiometer means in said housing means.

4. A potentiometer according to claim 2, in which said reciprocatory actuator rod means comprises an elongate rod having a portion extending through and reciprocatory in said bearing and said portion being of diameter of the order of not less than one third the outside diameter of said cylinder, whereby said potentiometer can be exceptionally long and slender without detriment to operability.

5. A potentiometer according to claim 2, in which said support means presents on said exterior surface thereof at least one longitudinally-extending conductor-receiving groove and a transverse slot interconnecting said first mentioned groove and said conductor receiving groove, and in which potentiometer said third means comprises a terminal conductor disposed in said conductor-receiving groove, said terminal conductor connected via said transverse slot to a point on said resistance element intermediate the ends of the latter, whereby an intermediate tap connection of said resistance elemetn is provided.

6. A potentiometer according to claim 2, in which said conductive contact device comprises a third contact brushing on said elongate return conductor, whereby to ensure continuous electrical contact with said return conductor.

References Cited UNITED STATES PATENTS 2,850,608 9/1958 Bourns et al 338-183 3,030,599 4/1962 Bourns et a1 338183 3,124,780 3/1964 Hulbert 338--l83 ROBERT K. SCHAEFER, Primary Examiner.

H. I. HOHAUSER, Assistant Examiner. 

1. AN ELONGATE SLENDER LINEAR POTENTIOMETER CHARACTERIZED BY SMALL MAXIMUM TRANSVERSE DIMENSION AND INEXPENSIVE CONSTRUCTION, SAID POTENTIOMETER COMPRISING: FIRST MEANS, INCLUDING HOUSING MEANS FORMED PRINCIPALLY AS AN ELONGATE CYLINDER AND A BEARING IN A FIRST END THEREOF; SECOND MEANS, INCLUDING AN ELONGATE SUPPORT MEANS HAVING AN ELONGATE EXTERIOR SURFACE COMPLEMENTARY WITH AND CLOSELY FITTING A PORTION OF THE ELONGATE INTERIOR SURFACE OF SAID CYLINDER, SAID SUPPORT MEANS PRESENTING ALONG ITS EXTERIOR AN ELONGATE GROOVE AND PRESENTING FURTHER AN ELONGATE GUIDEWAY; THIRD MEANS, INCLUDING A RESISTANCE ELEMENT SUPPORTED IN SAID ELONGATE GROOVE WITH A CONTACT SURFACE EXPOSED FOR BRUSHING OF A CONTACT THEREON, AN ELONGATE RETURN CONDUCTOR SUPPORTED ON THE EXTERIOR OF SAID SUPPORT MEANS GENERALLY PARALLEL TO SAID RESISTANCE ELEMENT, AND TERMINAL MEANS FOR SAID ELEMENT AND SAID CONDUCTOR; FOURTH MEANS, INCLUDING RECTILINEARLY MOVABLE MEANS COMPRISING A SLIDER DEVICE OPERABLE ALONG AND ENGAGING SAID GUIDEWAY TO BE GUIDED THEREBY, AND SAID SLIDER DEVICE COMPRISING A CONDUCTIVE CONTACT DEVICE HAVING A FIRST CONTACT IN BRUSHING ENGAGEMENT WITH SAID ELONGATE CONDUCTOR AND A SECOND CONTACT IN BRUSHING ENGAGEMENT WITH THE SAID CONTACT SURFACE OF SAID RESISTANCE ELEMENT; AND FIFTH MEANS, INCLUDING RECIPROCATORY ACTUATOR ROD MEANS EXTENDING THROUGH SAID BEARING AND CONNECTED TO SAID SLIDER DEVICE FOR RECIPROCATION OF THE LATTER ALONG SAID GUIDEWAY; WHEREBY SAID SECOND, THIRD, FOURTH AND FIFTH MEANS CAN BE ASSEMBLED TO FORM AN OPERABLE SUBASSEMBLY AND SUBJECTED TO OPERATING AND ELECTRICAL TESTS WITH THE COMPONENTS THEREOF EXPOSED FOR VISUAL INSPECTION AND ACCESS, PRIOR TO INCORPORATION OF SAID SECOND, THIRD AND FOURTH MEANS IN SAID CYLINDER AND ASSEMBLY WITH SAID FIRST MEANS TO FORM A COMPLETE POTENTIOMETER. 